Relaxation of spherical systems with long-range interactions: a numerical investigation

The process of relaxation of a system of particles interacting with long-range forces is relevant to many areas of Physics. For obvious reasons, in Stellar Dynamics much attention has been paid to the case of 1/r^2 force law. However, recently the interest in alternative gravities emerged, and significant differences with respect to Newtonian gravity have been found in relaxation phenomena. Here we begin to explore this matter further, by using a numerical model of spherical shells interacting with an 1/r^alpha force law obeying the superposition principle. We find that the virialization and phase-mixing times depend on the exponent alpha, with small values of alpha corresponding to longer relaxation times, similarly to what happens when comparing for N-body simulations in classical gravity and in Modified Newtonian Dynamics.Comment: 6 pages, 3 figures, accepted in the International Journal of Bifurcation and Chao

Tomography of Collisionless Stellar Systems

In this paper the concept of tomography of a collisionless stellar system of general shape is introduced, and a generalization of the Projected Virial Theorem is obtained. Applying the tomographic procedure we then derive a new family of virial equations which coincides with the already known ones for spherically symmetric systems. This result is obtained without any use of explicit expressions for the line-of-sight velocity dispersion, or spherical coordinate system.Comment: BAP-06-1994-016-OAB. 7 pages, postscript file. In press on Celestial Mechanic

Galactic cannibalism in the galaxy cluster C0337-2522 at z=0.59

According to the galactic cannibalism model, cD galaxies are formed in the center of galaxy clusters by merging of massive galaxies and accretion of smaller stellar systems: however, observational examples of the initial phases of this process are lacking. We have identified a strong candidate for this early stage of cD galaxy formation: a group of five elliptical galaxies in the core of the X-ray cluster C0337-2522 at redshift z=0.59. With the aid of numerical simulations, in which the galaxies are represented by N-body systems, we study their dynamical evolution up to z=0; the cluster dark matter distribution is also described as a N-body system. We find that a multiple merging event in the considered group of galaxies will take place before z=0 and that the merger remnant preserves the Fundamental Plane and the Faber-Jackson relations, while its behavior with respect to the Mbh-sigma relation is quite sensitive to the details of black hole merging [abridged].Comment: 30 pages, 7 figures, MNRAS (accepted

Decoupled and inhomogeneous gas flows in S0 galaxies

A recent analysis of the "Einstein" sample of early-type galaxies has revealed that at any fixed optical luminosity Lb S0 galaxies have lower mean X-ray luminosity Lx per unit Lb than ellipticals. Following a previous analytical investigation of this problem (Ciotti & Pellegrini 1996), we have performed 2D numerical simulations of the gas flows inside S0 galaxies in order to ascertain the effectiveness of rotation and/or galaxy flattening in reducing the Lx/Lb ratio. The flow in models without SNIa heating is considerably ordered, and essentially all the gas lost by the stars is cooled and accumulated in the galaxy center. If rotation is present, the cold material settles in a disk on the galactic equatorial plane. Models with a time decreasing SNIa heating host gas flows that can be much more complex. After an initial wind phase, gas flows in energetically strongly bound galaxies tend to reverse to inflows. This occurs in the polar regions, while the disk is still in the outflow phase. In this phase of strong decoupling, cold filaments are created at the interface between inflowing and outflowing gas. Models with more realistic values of the dynamical quantities are preferentially found in the wind phase with respect to their spherical counterparts of equal Lb. The resulting Lx of this class of models is lower than in spherical models with the same Lb and SNIa heating. At variance with cooling flow models, rotation is shown to have only a marginal effect in this reduction, while the flattening is one of the driving parameters for such underluminosity, in accordance with the analytical investigation.Comment: 32 pages LaTex file, plus 5 .ps figures and macro aasms4.sty -- Accepted on Ap

Asymmetric Gravitational Lenses in TeVeS and Application to the Bullet Cluster

Aims: We explore the lensing properties of asymmetric matter density distributions in Bekenstein's Tensor-Vector-Scalar theory (TeVeS). Methods: Using an iterative Fourier-based solver for the resulting non-linear scalar field equation, we numerically calculate the total gravitational potential and derive the corresponding TeVeS lensing maps. Results: Considering variations on rather small scales, we show that the lensing properties significantly depend on the lens's extent along the line of sight. Furthermore, all simulated TeVeS convergence maps strongly track the dominant baryonic components, non-linear effects, being capable of counteracting this trend, turn out to be very small. Setting up a toy model for the cluster merger 1E0657-558, we infer that TeVeS cannot explain observations without assuming an additional dark mass component in both cluster centers, which is in accordance with previous work.Comment: LaTex, 14 pages, 10 figures, references added, 2 figures removed, minor text changes to fit accepted version (A&A

Modelling elliptical galaxies: phase-space constraints on two-component (gamma1,gamma2) models

In the context of the study of the properties of the mutual mass distribution of the bright and dark matter in elliptical galaxies, present a family of two-component, spherical, self-consistent galaxy models, where one density distribution follows a gamma_1 profile, and the other a gamma_2 profile [(gamma_1,gamma_2) models], with different total masses and ``core'' radii. A variable amount of Osipkov-Merritt (radial) orbital anisotropy is allowed in both components. For these models, I derive analytically the necessary and sufficient conditions that the model parameters must satisfy in order to correspond to a physical system. Moreover, the possibility of adding a black hole at the center of radially anisotropic gamma models is discussed, determining analytically a lower limit of the anisotropy radius as a function of gamma. The analytical phase-space distribution function for (1,0) models is presented, together with the solution of the Jeans equations and the quantities entering the scalar virial theorem. It is proved that a globally isotropic gamma=1 component is consistent for any mass and core radius of the superimposed gamma=0 model; on the contrary, only a maximum value of the core radius is allowed for the gamma=0 model when a gamma=1 density distribution is added. The combined effects of mass concentration and orbital anisotropy are investigated, and an interesting behavior of the distribution function of the anisotropic gamma=0 component is found: there exists a region in the parameter space where a sufficient amount of anisotropy results in a consistent model, while the structurally identical but isotropic model would be inconsistent.Comment: 29 pages, LaTex, plus 5 .eps figures and macro aaspp4.sty - accepted by ApJ, main journa

The importance of dry and wet merging on the formation and evolution of elliptical galaxies

With the aid of a simple yet robust approach we investigate the influence of dissipationless and dissipative merging on galaxy structure, and the consequent effects on the scaling laws followed by elliptical galaxies. Our results suggest that ellipticals cannot be originated by parabolic merging of low mass spheroids only, even in presence of substantial gas dissipation. However, we also found that scaling laws such as the Faber-Jackson, Kormendy, Fundamental Plane, and the Mbh -sigma relations, when considered over the whole mass range spanned by ellipticals in the local universe, are robust against merging. We conclude that galaxy scaling laws, possibly established at high redshift by the fast collapse in pre-existing dark matter halos of gas rich and clumpy stellar distributions, are compatible with a (small) number of galaxy mergers at lower redshift.Comment: 31 pages, 7 figures, accepted by ApJ (main journal

The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?

We examine the properties of a morphologically-selected sample of 0.4<z<1.0 spheroidal galaxies in the GOODS fields in order to ascertain whether their increase in abundance with time arises primarily from mergers. To address this question we determine scaling relations between the dynamical mass determined from stellar velocity dispersions, and the stellar mass determined from optical and infrared photometry. We exploit these relations across the larger sample for which we have stellar masses in order to construct the first statistically robust estimate of the evolving dynamical mass function over 0<z<1. The trends observed match those seen in the stellar mass functions of Bundy et al. 2005 regarding the top-down growth in the abundance of spheroidal galaxies. By referencing our dynamical masses to the halo virial mass we compare the growth rate in the abundance of spheroidals to that predicted by the assembly of dark matter halos. Our comparisons demonstrate that major mergers do not fully account for the appearance of new spheroidals since z~1 and that additional mechanisms, such as morphological transformations, are required to drive the observed evolution.Comment: Accepted to ApJL; New version corrects the Millennium merger predictions--further details at http://www.astro.utoronto.ca/~bundy/millennium

Origin of the 2009 Mexico influenza virus: a comparative phylogenetic analysis of the principal external antigens and matrix protein

Triple-reassortant swine influenza A (H1) viruses, containing genes from avian, human, and swine influenza viruses, emerged and became an outbreak among humans worldwide. Over a 1,000 cases were identified within the first month, chiefly in Mexico and the United States. Here, the phylogenetic analysis of haemagglutin (HA), neuraminidase (NA), and matrix protein (MP) was carried out. The analysis showed that the H1 of this reassortant originated from American pigs, while NA and MP were more likely from European pigs. All of the 2009 isolates appear homogeneous and cluster together, although they are distinct from classical human A (H1N1) viruses

RECOVERING THE INTRINSIC METALLICITY DISTRIBUTION OF ELLIPTICAL GALAXIES

We address the problem of deriving, from the observed projected metallicity gradients, the intrinsic metallicity distribution of elliptical galaxies as a function of their integrals of motion. The method is illustrated by an application to anisotropic spherical Hernquist models. We also compare the derived metallicity distribution with those expected from two very simple models of galaxy formation and find that the more dissipative scheme agrees better with the typical metallicity distribution of ellipticals.Comment: 3 pages, Postscript file, 1 figure available upon request from [email protected]